The present invention relates to superconducting free electron laser.
Free electron lasers are promising devices which can produce coherent and directional radiation at variable wavelengths. The free electron laser can emit laser rays by making use of an electron beam passed through a periodical magnetic field (referred to as "wiggler" for short hereinbelow). Electrons running through a wiggler are waved in accordance with the periodical change of the magnetic field in the wiggler and emit laser rays in phase. The radiation successfully emitted from prior art free electron lasers has been only limited to infrared or millimeter wavelength ranges. The wavelength W of laser rays in accordance with the free electron laser is given by EQU W.about.Wo/2r
where
Wo is the periodical length of the wiggler, PA1 r=[1-(v/c).sup.2 ].sup.-1/2 PA1 v is the speed of electrons and c is the light speed.
In most cases, wigglers are induced by permanent magnetos and therefore the periodical unit length W is limited to the order of several centimeters. Because of this, when emission of a visible light is desired, it is necessary to accelerate electrons at a very high energy as 100 MeV. Such a high energy requires a very large size accelerator which is inconvenient for industrial and R&D use.
The wavelength of laser rays can be made shorter by use of a wiggler having a shorter periodical unit length. However, the shorter the periodic length is, the lower the magnetic field strength and therefore the emission efficient becomes. At the present, only a maximum conversion efficient of 40% has been attained while the existence of laser emission have been confirmed at a shortest wavelength of 0.5 micron.